Sterols, phospholipids and fatty acids of lenses of triparanol fed rats will be studied at several intervals during the triparanol feeding period before cataracts appear and for 3 to 6 weeks after appearance of mature cataracts. These measurements will be related to ATPase activity of the lenses and to area-surface pressure measurements on the lipid films. Similar studies will be performed on galactose cataracts, irradiation cataracts and human senile cataracts and on normal lenses of the same age. The results will be used to determine with more certainty if the influx of Na positive ions and water, which accompanies cataract formation, is due to failure of an active sodium pump, increase passive permeability, or both, resulting from changes in the lipid composition of the lens fiber membranes.